1. Field of the Invention
The present invention relates to data stream parsers. More particularly, the present invention relates to the field of parsing techniques to facilitate decoding a data stream.
2. Related Art
Digital transmission techniques have evolved to provide a multitude of options to a receptive television audience. Information digitally transmitted via satellite, cable, or terrestrial transmitters can have TV programs (e.g., video and audio) as well as interactive programs and additional data material (e.g., audio in multiple languages, text for the hearing impaired, etc.). Typically, the digital transmission (e.g., a data stream having many packets) is scrambled to protect intellectual property rights and to limit the reception of the digital transmission to a television audience that has paid for the right to receive the digital transmission. A variety of unauthorized techniques have evolved to descramble the data stream without permission.
As a result, emphasis had been placed in improving data security within an authorized receiver such as a set top box. In particular, a set top box having a higher level of data security facilitates protecting intellectual property rights and limiting the reception of the data stream to a television audience that has paid for the right to receive the data stream. A variety of data security techniques have been implemented.
However, many of these data security techniques interfere with the decoding of the data stream. For example, within the set top box, the data stream may remain encrypted even when transferred from one location to another location in the set top box. Thus, the processor of the set top box has to decrypt and scan the data stream so that to send the appropriate portion of the encrypted data stream to the decoder of the set top box. For example, during Trick Mode operation (e.g., fast forward, fast reverse, etc.), only packets having particular MPEG video frames are sent to a MPEG decoder. Unfortunately, this decryption/scanning procedures can overwhelm the processor and slow down the speed of decoding the data stream. Moreover, the unauthorized techniques can exploit the processor's ability to decrypt the data stream. In another implementation, the processor of the set top box is unable to decrypt the encrypted data stream. Hence, the processor has to send most of the encrypted data stream to the decoder, forcing the decoder to decrypt and to scan the data stream to locate the appropriate portion of the data stream (e.g., for supporting a Trick Mode operation). The decryption/scanning procedures overwhelm the decoder and slow down the speed of decoding the data, sometimes preventing the data from being decoded.